Ionization fire detection device

ABSTRACT

A fire detection device comprising an enclosure enclosing a reference ionization chamber and an unsaturated measuring ionization chamber interconnected in series and each containing a source of radioactive radiations, at least one alarm and/or automatic intervention device, a grid permeable to gases defining one end of the enclosure, the enclosure having apertures communicating with passages at one end of the unsaturated chamber so that gas can flow through the unsaturated chamber, from outside the device, a common electrode extending into both chambers and a printed circuit controlling the alarm and/or intervention device.

United States Patent lnventor Christian Marie Maurice Bertrand PonsarParis, France Appl. No. 703,348 Filed Feb. 6, 1968 Patented June 1, 1971Assignee Vigifeu Aubervilliers, France Priority Feb. 9, 1967 France94-266 IONIZATION FIRE DETECTION DEVICE 15 Claims, 3 Drawing Figs.

- 250/44, 313/54, 340/237 lnt.Cl ..G0ln 23/12 Field of Search 250/43.5D,

[56] References Cited UNITED STATES PATENTS 2,963,600 12/1960 Meili etal.... 313/54 2,994,768 8/1961 Derfler 250/43.5D 3,382,364 5/1968Guilleux 250/44 Primary Examiner-Archie R. Borchelt Anorney Wenderoth,Lind & Ponack ABSTRACT: A fire detection device comprising an enclosureenclosing a reference ionization chamber and an unsaturated measuringionization chamber interconnected in series and each containing a sourceof radioactive radiations, at least one alarm and/0r automaticintervention device, a grid permeable to gases defining one end of theenclosure, the enclosure having apertures communicating with passages atone end of the unsaturated chamber so that gas can flow through theunsaturated chamber, from outside the device, a common electrodeextending into both chambers and a printed circuit controlling the alarmand/or intervention device.

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IONIZATION FIRE DETECTION DEVICE The present invention relates todevices ascertaining the start ofa fire by the detection of variationsin the composition of a gas, and in particular the presence of smoke inthe atmosphere.

These devices usually comprise detectors proper which are disposed insuitable chosen places in a building or an installation and which, whenexcited by a sufficiently large modification in the surroundingconditions, actuate an alarm device and/or an automatic interventiondevice.

It is known to provide in this type of such detection devices anionization chamber which is connected in series to an open unsaturatedionization chamber which the surrounding atmosphere enters and in whichionization of the gas varies with its composition. This compositionvaries in particular when the fumesor smokes of combustion are given offand enter the open chamber. The variation in the degree of ionization inthis chamber is manifested by a variation in a measurable electricmagnitude by applying a voltage between the walls of these chambers, onone hand, and a common electrode on the other, and by connecting thiselectrode to a suitable electric circuit. A constant bipolar ioniccurrent passes into the closed chamber, whereas in the open chamber thiscurrent depends on the composition of the gas therein. The potential ofthe common electrode varies therefore and constitutes the electricmagnitude used in the circuit for actuating the alarm device.

For ionizing the gas contained in the chambers there is employed asource of radioactive radiation and, in known devices, the radioactivityof this source must be high, for example of the order ofa few tens ofmicrocuries. Further, the voltages which must be applied between thewall of the ionization chambers and their electrode are rather high,exceeding 200 v. in most cases.

This same drawback, but in a more serious form, is found in detectingdevices in which a unipolar current is produced in one of the chambersby sending in at least one part of this chamber only charged carriers ofthe same sign.

The object of the invention is to provide a detection device which isdevoid of the drawbacks of known devices, simple and particularlyreliable in operation.

The invention provides a fire detection device comprising a referenceionization chamber and an unsaturated measuring ionization chamberinterconnected in series and each containing a source of radioactiveradiation, at least one alarm and/or automatic intervention device, anenclosure defined at one end by a grid which is permeable to the gasesand encloses said ionization chambers, said unsaturated chambercommunicating through one end with the space defined by said grid andhaving at its other end passages which communicate with the vicinity ofapertures formed in said enclosure, whereby the gas surrounding thedetector passes in said unsaturated chamber, a common electrodeextending into both of said chambers, said enclosure also enclosing aprinted circuit plate which carries a circuit controlling the alarmdevice.

According to another embodiment of the invention, the control circuitcomprises the electrode common to the two ionization chambers connectedthrough an amplifying device to the gate electrode of a triggering oractuating switch inserted in the feed circuit of the alarm device.

The amplifying device comprises a transistor the base of which isconnected to the common electrode and the switch can be a thyristorwhose gate electrode is connected to the emitter of the transistor.

Another object of the invention is to provide a fire detectioninstallation comprising a plurality of detection devices definedhereinbefore which are connected in parallel to a line having threeconductors one of which has a positive potential. the second a zeropotential and the third a negative potential, a first alarmdeviceresponsive to the triggering of the switch of any one of the detectiondevices, and a second alarm device which is actuated when a break occursin the line.

Further features and advantages of the invention will be apparent fromthe ensuing description with reference to the accompanying drawings.

in the drawings:

FIG. 1 is a longitudinal sectional view of a preferred embodiment ofafire detection device according to the invention;

FIG. 2 is a circuit diagram of an installation comprising detectiondevices of the type shown in FIG. 1, with a more detailed circuitdiagram of one of said detection devices, and

FIG. 3 is a view similar to FIG. 1 of said a detection device in aslightly simplified form.

The invention will be described and its operation explained withreference to FIGS. 1 and 2 of the drawings. FIG. 1 shows a detectiondevice D which is defined externally by a cylindrical enclosure 1 and agrid 2 of metal fabric or plastics material in the shape of a sphericaldome.

Mounted in the enclosure 1 is an ionization chamber 3 whose cylindricalwall 3 constitutes an electrode spaced from the enclosure by aninsulating ring 4. One end 3 of this chamber freely communicates withthe space defined by the grid 2. At its other end 3 the chamber 3 isprovided with an end wall having apertures 3 which communicate with thevolume of the enclosure 1 in the vicinity of apertures 1 formed in thelatter so as to ensure a flow of the surrounding air in the chamber 3.

The chamber 3 contains, fixed to its lateral wall, a radioactive source5 having a radioactivity of the order of a few microcuries.

A second chamber 6 is connected to the first chamber through insulatingspacer members 7. This chamber 6 has a wall 6 which is substantiallyclosed and nonresponsive to surrounding conditions and also contains atleast one radioactive source 6', 6 The wall 6" of this chamberconstitutes an electrode in the same way as the wall 3" ofthe firstchamber 3.

An electrode 8 is located between the two chambers 3 and 6 and extendsinto each of them. In the presently described embodiment, this electrodeis fixed to the wall of the chamber 6 through an insulating support 9and carries a disc 10 in the part thereof extending into the chamber 3for deforming the field lines within the chamber 3.

A plate 11 of a printed circuit is mounted on the chamber 6 by means ofspacer members 12 near the inner end of the chamber 1, this platecarrying various electric and electronic components of the controlcircuit shown at D in FIG. 2.

The chamber 1 is closed at its rear or inner end by an insulating disc13.

Most of the components of the control circuit have been purposely leftout of the FIG. 1 and will be described with reference to FIG. 2 whichshows the diagram of an installation which comprises in particular ndetection devices D D D similar to the detection device D shown in FIG.1.

As seen in the circuit diagram, the measuring electrode 8 is connectedto the base of a transistor 14 whose collector is brought to a positivepotential and whose emitter is connected through a resistor 15 connectedin series with the gate electrode of a thyristor 16. A filter capacitor17 is connected between the gate electrode and the cathode of thethyristor.

interposed between the anode of this thyristor and a conductor L ofaline L, brought to a positive potential, is a lamp 118 to which isconnected in parallel a Zener diode 19.

The line L comprises three conductors L of positive potential, L ofnegative potential-to which the wall 3 of the chamber 3 is connectedthrough a potentiometer 20 the latter being connected to the conductor Lthrough a resistor 21- -and a neutral conductor L The lamp 18, the diode19, the collector of the transistor 14, the wall 6 of the chamber 6 andthe resistor 21 are connected to the conductor L,.

The cathode of the thyristor l6 and the grid 2 are connected to theconductor L the grid being consequently at zero potential.

Each detector D,, 0,, D is connected to the conductors L,, L L, of theline L through three conductors C,, C C

An end-of-line resistor 22 and a coil 23 in the conductor L are alsoprovided. As will be understood hereinafter, the coil 23 serves toexcite the two contacts 24, 25 having different characteristics whichare preferably relays of the reed" or double-position type. Thesecontacts 24, 25 actuate alarm devices 26, 27 respectively.

The detection device and the installation operate in the followingmanner:

At rest, that is, when the atmosphere surrounding the detection deviceis normal, the walls 3 and 6 of the chambers 3 and 6 are respectivelybrought to negative and positive potentials, the electrode 8 being at anintermediate potential which is insufficient to excite the base of thetransistor 14 and render it conductive.

It should be mentioned that the potentiometer assembly 20, 21 permitsbringing the wall 3 to a predetermined potential as a function of thecharacteristics required of this detection device, and thus setting thedetection threshold of each detection device.

Under normal conditions, the leakage current which circulates betweenthe collector and the emitter of the transistor is insufficient toactuate the thyristor 16.

In the detector proper (FIG. 1) air flows in the chamber 3, between thegrid 2, which defines what might be called a collection chamber, and theapertures l in the enclosure 1.

If particles of smoke are contained in a sufficient number in the airpassing through the chamber 3, the ionization conditions change in thischamber and the potential of the electrode 8 reaches a magnitudesufficient to render the transistor 14 conductive. The latter performsthe function of an amplifier, which is necessary owing to the very smallcurrent values, namely of the order of I A, employed in the ionizationchambers.

The current supplied by the emitter of the transistor 14 actuates thethyristor l6, and causes the passage of the current in the signal lampl8 and the increase in the current which passes through the coil 23.

The lamp 18 lights up and this supplies a first alarm signal by theillumination of the detector since this lamp is within the enclosure 1(FIG. 1).

Simultaneously, the current increase in the coil 23 actuates the contact24 and feeds the alarm device 26 which is located at a certain distancefrom the points of detection.

The Zener diode 19 is adapted to permit the passage of a current to thecoil 23 in the event that there is a break in the lamp 18.

Two other safety devices are employed in this installation. A transistorhaving a field effect and whose input impedance decreases with thetemperature, is employed as transistor 14, the leakage current doublingfor example for an increase in temperature of about C. For apredetermined temperature of the order of 60 C. for example, thisleakage current becomes sufficient to actuate the thyristor 16. Thedevice operates therefore also as a temperature limiter in case thepresence ofsmoke had not be detected.

The other safety device consists of the relay and the alarm device 27which operates in response to a break in the line. The latter isconsequently completely supervised.

The special arrangement of the detection device shown in FIG. I affordsa number of advantages. The reception of the surrounding air and smokeoccurs through the grid 2 and in the the space the latter defines, andthis air and smoke pass through the chamber 3 and thereafter issue byway of the apertures 1. According to the conditions, the opposite pathcould be taken, but in both cases the fact that the air is not directlyreceived or collected by the measuring chamber is important. Indeed,this permits reducing the dimensions of this chamber and consequentlydecreasing the radioactivity of the source 5 and the voltage applied.The diameter of the chamber can even be less than the free mean path ofthe ionizing particles. The voltage applied to each of the chambers isaround 50 v. and the radioactivity of the source 5 is generally lessthan 5 microcuries.

Further, the result of this arrangement, at least in part, is that thedetection device according to the invention is little responsive tovariations in density and variations in the rate of flow of the gaseswithin the ionization chamber.

Further, the measuring ionization chamber is not in direct contact withthe atmosphere and is thus protected. Another advantage of thisdetection device is that the outer part of the device, namely theenclosure and grid, are at zero potential and this satisfies safetyregulation requirements.

FIG. 3 shows a simplified modification of the detection device proper inwhich the saturated ionization chamber 6 of the first embodiment iseliminated. This saturated chamber is here defined by the grid 2 and adisc 28 carried by the electrode 8 and on which is placed a radioactivesource 29.

The electric circuit diagram is somewhat modified, the grid no longerbeing at zero potential but at the potential to which the wall of thechamber 6 of the first embodiment was brought. This is a slight drawbackcompared to the first embodiment described. Apart from this, the wiringand the operation are the same as described hcreinbefore.

Although specific embodiments of the invention have been described, manymodifications and changes may be made therein without departing from thescope of the invention as defined in the appended claims.

Having now described my invention what I claim as new and desire tosecure by Letters Patent is:

l. A fire detection device comprising an enclosure, a grid at one end ofthe enclosure, which is permeable to gases and defines a gas collectionspace, a reference ionization chamber and an unsaturated measuringionization chamber, said chambers being connected in series and eachcontaining a source of radioactive radiation for ionizing the gastherein, said enclosure having apertures in its lateral wall, saidunsaturated measuring chamber being located in said enclosure andopening at one end in the gas collection space defined by said grid andhaving at its other end passages which communicate with said apertures,whereby the gas surrounding the detection device can flow through saidunsaturated measuring chamber, a common electrode extending into both ofsaid chambers, and having an intermediate point thereof connected in anelectric control circuit including alarm means and being responsive tochanges in the ionization in said unsaturated chamber and reacting tosaid changes.

2. A fire detection device as claimed in claim 1, wherein said circuitcomprises said electrode which is common to said two ionizationchambers, a transistor whose base is connected to said intermediatepoint of the common electrode and a gate controlled switch connected inthe feed circuit of said alarm means, the gate of said switch beingconnected to the emitter of said transistor.

3. A fire detection device as claimed in claim 2, wherein said gatecontrolled switch is a thyristor.

4. A fire detection device as claimed in claim 1, wherein said alarmmeans comprise a signal lamp located within said enclosure.

5. A fire detection device as claimed in claim 1, comprising, on a partof said common electrode located in said unsaturated chamber, a discwhich deforms the field lines inside said unsaturated measuring chamber.

6. A fire detection device as claimed in claim 1, wherein said grid isbrought to zero potential.

7. A fire detection device as claimed in claim I, wherein current issupplied to the unsaturated measuring chamber through a potentiometercircuit for setting the detection threshold of the detector.

8. A fire detection device as claimed in claim 1, wherein saidunsaturated ionization chamber has a diameter less than the free meanpath of the ionizing particles.

9. A fire detection device as claimed in claim I, wherein said commonelectrode carries a disc which defines a chamber with said grid, apassage being provided around said disc for communication with themeasuring chamber, said disc carrying a radioactive source on the facethereof facing said grid so that said chamber constitutes the referencechamber and the gas collection space.

10. A fire detection device as claimed in claim 3, wherein saidtransistor has an input impedance whose temperature coefficient isnegative and which is adapted to actuate said switch when apredetermined temperature is reached,

11. A fire detection device comprising an enclosure, a grid at one endof the enclosure, which is permeable to gases and defines a gascollection space, a reference ionization chamber and an unsaturatedmeasuring ionization chamber, said chambers being connected in seriesand each containing a source of radioactive radiation for ionizing thegas therein, said enclosure having apertures in its lateral wall, saidunsaturated measuring chamber being located in said enclosure andopening at one end in the gas collection space defined by said grid andhaving at its other end passages which communicate with said apertures,whereby the gas surrounding the detection device can flow through saidunsaturated measuring chamber, a common electrode extending into both ofsaid chambers, and having an intermediate point thereof connected in acontrol cirionization cuit, said control comprising in each detectiondevice, a transistor and a gate controlled switch, the transistor havingits base connected to said intermediate point of the correspondingcommon electrode, and its emitter connected to the gate of said switch;a first alarm device responsive to actuation of said switch of any ofsaid detection devices and a second alarm device which is combined withsaid line and adapted to be actuated when a break in said line occurs.

12. An installation as claimed in claim 11, wherein each of saiddetection devices includes a signal lamp and a Zener diode connected inparallel with the signal lamp between said switch and said line.

13. An installation as claimed in claim 11, wherein said alarm devicesare respectively actuated by a double-position or reed-type relay havingdifferent contact characteristics.

14. A fire detection device as claimed in claim 1, wherein saidenclosure is earthed or brought to zero potential.

15. A fire detection device as claimed in claim 1, wherein said grid hasa spherical dome shape.

1. A fire detection device comprising an enclosure, a grid at one end ofthe enclosure, which is permeable to gases and defines a gas collectionspace, a reference ionization chamber and an unsaturated measuringionization chamber, said chambers being connected in series and eachcontaining a source of radioactive radiation for ionizing the gastherein, said enclosure having apertures in its lateral wall, saidunsaturated measuring chamber being located in said enclosure andopening at one end in the gas collection space defined by said grid andhaving at its other end passages which communicate with said apertures,whereby the gas surrounding the detection device can flow through saidunsaturated measuring chamber, a common electrode extending into both ofsaid chambers, and having an intermediate point thereof connected in aneLectric control circuit including alarm means and being responsive tochanges in the ionization in said unsaturated chamber and reacting tosaid changes.
 2. A fire detection device as claimed in claim 1, whereinsaid circuit comprises said electrode which is common to said twoionization chambers, a transistor whose base is connected to saidintermediate point of the common electrode and a gate controlled switchconnected in the feed circuit of said alarm means, the gate of saidswitch being connected to the emitter of said transistor.
 3. A firedetection device as claimed in claim 2, wherein said gate controlledswitch is a thyristor.
 4. A fire detection device as claimed in claim 1,wherein said alarm means comprise a signal lamp located within saidenclosure.
 5. A fire detection device as claimed in claim 1, comprising,on a part of said common electrode located in said unsaturated chamber,a disc which deforms the field lines inside said unsaturated measuringchamber.
 6. A fire detection device as claimed in claim 1, wherein saidgrid is brought to zero potential.
 7. A fire detection device as claimedin claim 1, wherein current is supplied to the unsaturated measuringchamber through a potentiometer circuit for setting the detectionthreshold of the detector.
 8. A fire detection device as claimed inclaim 1, wherein said unsaturated ionization chamber has a diameter lessthan the free mean path of the ionizing particles.
 9. A fire detectiondevice as claimed in claim 1, wherein said common electrode carries adisc which defines a chamber with said grid, a passage being providedaround said disc for communication with the measuring chamber, said disccarrying a radioactive source on the face thereof facing said grid sothat said chamber constitutes the reference ionization chamber and thegas collection space.
 10. A fire detection device as claimed in claim 3,wherein said transistor has an input impedance whose temperaturecoefficient is negative and which is adapted to actuate said switch whena predetermined temperature is reached.
 11. A fire detection devicecomprising an enclosure, a grid at one end of the enclosure, which ispermeable to gases and defines a gas collection space, a referenceionization chamber and an unsaturated measuring ionization chamber, saidchambers being connected in series and each containing a source ofradioactive radiation for ionizing the gas therein, said enclosurehaving apertures in its lateral wall, said unsaturated measuring chamberbeing located in said enclosure and opening at one end in the gascollection space defined by said grid and having at its other endpassages which communicate with said apertures, whereby the gassurrounding the detection device can flow through said unsaturatedmeasuring chamber, a common electrode extending into both of saidchambers, and having an intermediate point thereof connected in acontrol circuit, said control comprising in each detection device, atransistor and a gate controlled switch, the transistor having its baseconnected to said intermediate point of the corresponding commonelectrode, and its emitter connected to the gate of said switch; a firstalarm device responsive to actuation of said switch of any of saiddetection devices and a second alarm device which is combined with saidline and adapted to be actuated when a break in said line occurs.
 12. Aninstallation as claimed in claim 11, wherein each of said detectiondevices includes a signal lamp and a Zener diode connected in parallelwith the signal lamp between said switch and said line.
 13. Aninstallation as claimed in claim 11, wherein said alarm devices arerespectively actuated by a double-position or reed-type relay havingdifferent contact characteristics.
 14. A fire detection device asclaimed in claim 1, wherein said enclosure is earthed or brought to zeropotential.
 15. A fire detection device as claimed in claim 1, whereinsaid grid has a spherical dome shape.